Notes on Colour

Primaries colours for painters

a typical naive illustration of paint mixing a typical naive illustration of paint mixing
These are typical of illustrations that purport to explain colour mixing.

Colour myths

There is no such thing as painters’ primaries. When people say the primary colour are red, yellow and blue, they usually mean one of four things, all of which are misleading:

  1. Some people use red and blue as the colour names for magenta and cyan when they are talking about the subtractive primaries.
  2. Some painters refer to the colours they use when they are mixing paint as if they obeyed different laws of perception from colours produced in any other way.
  3. Some commentators2 have a mystical belief in fundamental, unmixed colours which they fail to connect to evidence about human perception (or mixing paints).
  4. Most commonly, people refer arbitrarily to a particular set of paint colours which they have found to produce a usefully large range of hues This could be any one of many sets of primaries that work well enough to be accepted. We accept them, given the complexities of subtractive mixing and the forgiving nature of human vision.

There are clear physical reasons why colour mixing is not going to be consistent from one type of paint to another. Perceptually identical colours will mix in different ways if their pigments have different absorbtion spectra—if they are a metameric pair.